June 10, 2004: Like a canary in a mine, a microbe can often
sense environmental dangers before a human can. It's easy to see a
canary's reaction. But how can you can you tell what a microbe's feeling?
How can you coax a microbe to communicate?

One
way is to interface it to a silicon chip.

University of Tennessee microbiologist Gary Sayler and his colleagues
have developed a device that uses chips to collect signals from specially
altered bacteria. The researchers have already used these devices,
known as BBICs, or Bioluminescent Bioreporter Integrated Circuits,
to track pollution on earth. Now, with the support of NASA's Office
of Biological and Physical Research, they're designing a version for
spaceships.

Sayler's group, which includes Tennessee researchers Steve Ripp,
Syed Islam and Ben Blalock, as well as collaborators at JPL and the
Kennedy Space Center, has bioengineered microbes that glow blue-green
in the presence of contaminants. Then they joined those bacteria to
microluminometers--chips designed to measure the light.

What BBICs offer, explains Sayler, is a low-cost, low-energy way
to detect pollutants. They're tiny: each BBIC is about 2 mm by 2 mm,
and the entire device, including its power source, will probably be
about the size of a matchbox, and they monitor their surroundings
continuously.

NASA is interested in sensing contaminants because spaceships are
tightly sealed. Unseen fumes from scientific experiments or toxins
produced by molds and other biofilms can accumulate and pose a hazard
to astronauts. BBICs can be crafted to sense almost anything: ammonia,
cadmium, chromate, cobalt, copper, proteins, lead, mercury, PCBs,
ultrasound, ultraviolet radiation, zinc--the list goes on and on.

The system
is surprisingly rugged. Microbes thrive in a wide range of environments,
so it's possible to design BBICs that can survive in extreme or highly
contaminated surroundings. "They can actually do their job sitting
in things such as jet fuel-water mixtures," marvels Sayler.

Although
the microbes can protect themselves from toxins, they still have a
variety of needs--food, for example. Keeping them alive, Sayler says,
"is a significant portion of the work."

One problem is that microbes must be immobilized so that they remain
right next to the chip. The challenge, says Sayler, is trying to figure
out how to immobilize the microbes in such a way that they survive
as long as possible.

The researchers are testing various substances that will keep the
microbes in place. Something with good optical transparency is critical,
of course, so that if the microbes light up, the chip can perceive
that. The immobilant has to be porous, so that any contamination can
flow in, and reach the microbes. It has to contain nutrients for the
microbes to feed on. It has to allow the microbe enough, but not too
much, room. "We're basically trying to feed the immobilized organisms
in the matrix without them growing. We really don't want them to grow
very much, if at all. If they grow, it changes the total amount of
cells in the system, and it confounds the issue of how much light
corresponds to how much contaminant."

(There
needs to be about a few thousand microbes per chip, says Sayler, in
order to generate enough light. That's not as many as it seems, though
-- it's only about enough to cover the tip of a pin.)

Sayler
hopes to develop gels in which the microbes can be kept functional
for several months. The sensors would probably be attached to the
spaceship walls, continuously monitoring the ship's atmosphere. They'd
monitor themselves, too, to make sure that the microbes were still
viable. "We can electrically induce cells to make light, so we
can pulse the system every once in a while to see if the organisms
are still physiologically active."

"After,
say, six months, the chip would send a signal that says, 'oops, time
to replace your bug sensor.' An astronaut would go and get a freeze-dried
package of seed microbes, add a little moisture, and stick it in the
sensor." Nothing more has to be done until the next time the
signal goes off, six months later. It's a low maintenance system.

Below:
Gary Sayler is the director of the Center for Environmental Biotechnology
at the University of Tennessee, Knoxville. [More]

These
BBICs are useful on Earth, too. They can detect formaldehyde emitted
by pressed wood furniture or hard-to-detect molds often implicated
in sick building syndrome. "If this device works as planned,
it could turn out to be a very inexpensive kind of monitoring system,"
says Sayler. "You could go to your corner drugstore, buy one
of these, take it home and stick it up on your wall. It could tell
you whether your carpets are degassing, or whether you've got problems
like black mold."

Advanced BBICs could serve as bioterrorism monitors for Homeland
Security, as a means to detect DNA radiation-damage in astronauts,
or as a diagnostic tool for doctors. An example: Sayler envisions
BBICs as part of a treatment program for diabetics. An implantable
BBIC equipped with an on-chip radio transmitter could monitor blood
glucose levels and communicate with a remote insulin delivery system.
Such devices could also scan body-fluids for certain proteins that
signal tumors--in other words, an early warning system for cancer.

Much more research needs to be done before these ideas become reality.
Making BBICs work on spaceships is a good place to start.